/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Multisets.setCountImpl;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * This class provides a skeletal implementation of the {@link Multiset} interface. A new multiset
 * implementation can be created easily by extending this class and implementing the
 * {@link Multiset#entrySet()} method, plus optionally overriding {@link #add(Object, int)} and
 * {@link #remove(Object, int)} to enable modifications to the multiset.
 *
 * <p>
 * The {@link #count} and {@link #size} implementations all iterate across the set returned by
 * {@link Multiset#entrySet()}, as do many methods acting on the set returned by
 * {@link #elementSet()}. Override those methods for better performance.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 */
@GwtCompatible
abstract class AbstractMultiset<E> extends AbstractCollection<E> implements Multiset<E> {
    // Query Operations

    @Override
    public int size() {
        return Multisets.sizeImpl(this);
    }

    @Override
    public boolean isEmpty() {
        return entrySet().isEmpty();
    }

    @Override
    public boolean contains(@Nullable Object element) {
        return count(element) > 0;
    }

    @Override
    public Iterator<E> iterator() {
        return Multisets.iteratorImpl(this);
    }

    @Override
    public int count(@Nullable Object element) {
        for (Entry<E> entry : entrySet()) {
            if (Objects.equal(entry.getElement(), element)) {
                return entry.getCount();
            }
        }
        return 0;
    }

    // Modification Operations
    @CanIgnoreReturnValue
    @Override
    public boolean add(@Nullable E element) {
        add(element, 1);
        return true;
    }

    @CanIgnoreReturnValue
    @Override
    public int add(@Nullable E element, int occurrences) {
        throw new UnsupportedOperationException();
    }

    @CanIgnoreReturnValue
    @Override
    public boolean remove(@Nullable Object element) {
        return remove(element, 1) > 0;
    }

    @CanIgnoreReturnValue
    @Override
    public int remove(@Nullable Object element, int occurrences) {
        throw new UnsupportedOperationException();
    }

    @CanIgnoreReturnValue
    @Override
    public int setCount(@Nullable E element, int count) {
        return setCountImpl(this, element, count);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean setCount(@Nullable E element, int oldCount, int newCount) {
        return setCountImpl(this, element, oldCount, newCount);
    }

    // Bulk Operations

    /**
     * {@inheritDoc}
     *
     * <p>
     * This implementation is highly efficient when {@code elementsToAdd} is itself a
     * {@link Multiset}.
     */
    @CanIgnoreReturnValue
    @Override
    public boolean addAll(Collection<? extends E> elementsToAdd) {
        return Multisets.addAllImpl(this, elementsToAdd);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean removeAll(Collection<?> elementsToRemove) {
        return Multisets.removeAllImpl(this, elementsToRemove);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean retainAll(Collection<?> elementsToRetain) {
        return Multisets.retainAllImpl(this, elementsToRetain);
    }

    @Override
    public void clear() {
        Iterators.clear(entryIterator());
    }

    // Views

    private transient Set<E> elementSet;

    @Override
    public Set<E> elementSet() {
        Set<E> result = elementSet;
        if (result == null) {
            elementSet = result = createElementSet();
        }
        return result;
    }

    /**
     * Creates a new instance of this multiset's element set, which will be returned by
     * {@link #elementSet()}.
     */
    Set<E> createElementSet() {
        return new ElementSet();
    }

    @WeakOuter
    class ElementSet extends Multisets.ElementSet<E> {
        @Override
        Multiset<E> multiset() {
            return AbstractMultiset.this;
        }
    }

    abstract Iterator<Entry<E>> entryIterator();

    abstract int distinctElements();

    private transient Set<Entry<E>> entrySet;

    @Override
    public Set<Entry<E>> entrySet() {
        Set<Entry<E>> result = entrySet;
        if (result == null) {
            entrySet = result = createEntrySet();
        }
        return result;
    }

    @WeakOuter
    class EntrySet extends Multisets.EntrySet<E> {
        @Override
        Multiset<E> multiset() {
            return AbstractMultiset.this;
        }

        @Override
        public Iterator<Entry<E>> iterator() {
            return entryIterator();
        }

        @Override
        public int size() {
            return distinctElements();
        }
    }

    Set<Entry<E>> createEntrySet() {
        return new EntrySet();
    }

    // Object methods

    /**
     * {@inheritDoc}
     *
     * <p>
     * This implementation returns {@code true} if {@code object} is a multiset of the same size and
     * if, for each element, the two multisets have the same count.
     */
    @Override
    public boolean equals(@Nullable Object object) {
        return Multisets.equalsImpl(this, object);
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * This implementation returns the hash code of {@link Multiset#entrySet()}.
     */
    @Override
    public int hashCode() {
        return entrySet().hashCode();
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * This implementation returns the result of invoking {@code toString} on
     * {@link Multiset#entrySet()}.
     */
    @Override
    public String toString() {
        return entrySet().toString();
    }
}
